The field of the invention is optics, measuring and testing. The present invention is particularly concerned with an apparatus for exposure metering in mirror reflex cameras wherein an image projected by a picture taking lens onto an image plane is observed by means of a pentaprism through an ocular.
The state of the art of the present invention may be ascertained by reference to U.S. Pat. No. 3,612,703 and West German Published Application 28 26 947, equivalent to U.S. patent application Ser. No. 48,693, filed June 14, 1979, and now abandoned the disclosures of which are incorporated herein.
U.S. Pat. No. 4,188,102 is incorporated herein to show that the exit pupil can be deflected by changing the angles of the pentaprism 7.
It is known for instance from U.S. Pat. No. 3,612,703 to measure the required exposure on the one hand for an image field portion representative of the overall image field, the so-called "large-field metering", and on the other hand merely for an especially important image field section, the so-called "spot" or "selective metering". Switching from one metering system to the other takes place for instance by using an at least partly transmitting mirror feeding the light associated with the central image area to a first detector and the light associated with the remaining area to one or more further detectors of which the output signals are fed to the analyzing electronic circuitry singly or in combination, that is, in an electrically switchable manner.
On the other hand, it is also known, for example, from West German Published Application No. 28 26 947, to feed light by optical means such as switchable lens elements or stops to the photoelectric detectors either from the entire area or only from a partial area.
However, these known arrangements suffer from the drawback that the splitting of the light fluxes by an at least partly transmitting mirror degrades the brightness of the entire viewer image.